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'91 Chevy K1500 5.7L TBI AT/OD


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acemoondog
New User

Jun 30, 2005, 7:09 PM

Post #1 of 8 (9183 views)
'91 Chevy K1500 5.7L TBI AT/OD Sign In

This truck is driving me nuts. It has an intermittant problem where on a very slight acceleration (like if it is parked on a hill) it spits and sputters and darn near shuts off. It runs fine at highway speed. Have had it on a scanner...Map sensor showed 8Hg when a gauge showed 20. Replaced it, same thing. Back on scanner...O2 sensor showed it stayed up around the .72-.90 range and very seldom crossed below .44. It also took 15 min. to go into closed loop. Changed O2 sensor, It may have gotten worse! In between, I pushed on the EGR valve to make engine stumble and put in half a bottle of 104 octane boost. Last week I put plugs (all looked ok), wires (they were awful) air and fuel filter (fuel had a carmal color). Timing also appears to be OK. Getting a little fired up here....any ideas out there? Haven't checked the fuel pressure, but believe it has to be ok as it runs fine at high speed pull. Coil seemed to throw more of an orange spark than blue?

randy


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jun 30, 2005, 10:09 PM

Post #2 of 8 (9177 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

Just an idea---- unplug EGR and plug vacuum line and see it that makes a difference. You'll get a "check engine" code but it should still run. If that changes anything the EGR is suspect. If no change or improvement you havent lost a thing for trying. Good luck,



motorheadII
User

Jul 1, 2005, 4:03 PM

Post #3 of 8 (9162 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

If nothing else helps, try replacing the TPS.


Guest
Anonymous Poster
kwatt2010@yahoo.com

Jun 30, 2009, 11:33 AM

Post #4 of 8 (6160 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

another suspect problem could be the map sensor


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 30, 2009, 11:40 AM

Post #5 of 8 (6158 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

You have a rich condition that you have to get to the bottom of. Check your vacuum reading at idle and compare that to the reading at the MAP sensor. Also you can try unplugging one injector at a time and watch what the 0/2's do. You have to find out where it's getting it's excess fuel from.

You also want to check for a plugged exhaust. Disconnect it at the manifold to test it.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jun 30, 2009, 11:41 AM)


Loren Champlain Sr
Veteran / Moderator
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Jun 30, 2009, 12:45 PM

Post #6 of 8 (6148 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

As Hammer suggested, you need to get to the bottom of the rich condition. Fifteen minutes to go into closed loop is way too long. Check actual engine temperature. Could be that it is just running too darned cool. Without your wife's knowledge, use her candy thermometer to test. A pyrometer would be better, but... The engine should be running around 200F all of the time. Anything less is not good.
Loren
SW Washington


Hammer Time
Ultimate Carjunky / Moderator
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Jun 30, 2009, 1:09 PM

Post #7 of 8 (6147 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

Man, I just noticed this question is 4 years old. More wasted time.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Loren Champlain Sr
Veteran / Moderator
Loren Champlain Sr profile image

Jun 30, 2009, 1:11 PM

Post #8 of 8 (6145 views)
Re: '91 Chevy K1500 5.7L TBI AT/OD Sign In

I was just 'following the leader'. SmileSmileSmileSmileSmile
Loren
SW Washington






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